The present invention relates generally to implantable medical devices and in particular to the use of implantable medical devices for treating supraventricular tachyarrhythmias.
Clinically, atrial arrhythmias are one of the most frequently encountered of the cardiac arrhythmias. Annually, more than 500,000 individuals are diagnosed with atrial arrhythmias, including atrial fibrillation, flutter and tachycardia. While these conditions are not immediately life-threatening, they can lead to serious health risks if left untreated. These include the increased potential for developing chronic fibrillation, embolic strokes and for transferring the aberrant atrial electrical signals to the ventricles, which can result in ventricular tachycardia and/or ventricular fibrillation.
Treating atrial fibrillation has traditionally involved the use of antiarrhythmic agents. However, patients who have experienced only one episode or infrequent paroxysmal episodes of atrial fibrillation may not want the inconvenience of daily medication and follow-up. Alternatively, patients with recurrent episodes are at the highest risk for a thromboembolism and often are candidates for maintenance antiarrhythmic and anticoagulation therapies. This long-term therapy, however, can have potential drawbacks as chronic use of some antiarrhytmnic agents may have toxic side effects. As a result, effective alternatives to chronic pharmacological treatment have been sought.
Implantable atrial cardioverter/defibrillators are a potential solution to acutely treat atrial fibrillation. The implantable atrial cardioverter/defibrillators sense and analyze atrial cardiac signals to detect the occurrence of an atrial arrhythmia. Once an atrial arrhythmia is detected, the device can deliver a low energy discharge of cardioverting/defibrillating electrical energy across the atria of the heart in an attempt to terminate the arrhythmia and to restore normal sinus rhythm. In designing these devices, investigators have also proposed synchronizing the delivery of the atrial defibrillation pulse to the sinus rhythm of the ventricles so as to avoid triggering a ventricular arrhythmia. While these suggested methods attempt to prevent inducing a ventricular arrhythmia, there remains the possibility of inducing a ventricular tachyarrhythmia or a ventricular fibrillation by inadvertently delivering a cardioverting/defibrillating electrical energy pulse during a T-wave that resulted from an aberrant ventricular contraction. Therefore, a need still exists for a system to safely and reliably treat a supraventricular arrhythmia.
The present invention provides an improved defibrillation system and method for safely and reliably treating supraventricular arrhythmias. The defibrillation system and method respond to a detected supraventricular arrhythmia by delivering a train of atrial pacing pulses and a series of ventricular pacing pulses in a synchronized manner. The invention is unique in that the defibrillation system synchronizes and coordinates the ventricles and the atria of the heart using the synchronized pacing pulses prior to defibrillating the atria such that the defibrillation electrical energy pulse is delivered so as to avoid occurring during a ventricular T-wave, thus reducing the likelihood of inducing a ventricular tachyarrhythmia or ventricular fibrillation.
According to one embodiment of the present invention there is provided a system including an implantable housing; a ventricular catheter; an atrial catheter; and electronic control circuitry within the implantable housing and coupled to the ventricular and atrial catheters for identifying and analyzing cardiac signals and for providing electrical energy to the heart to affect sinus rhythm of the heart in response to a signal from the electronic control circuitry indicating the occurrence of an atrial arrhythmia.
The ventricle catheter of the defibrillator system has at least one ventricular pacing electrode on its peripheral surface, which is electrically connected to the electronic control circuitry within the implantable housing. In one embodiment, the ventricular catheter has a first ventricular electrode and a second ventricular electrode for sensing and pacing the ventricle of the heart. In an additional embodiment, the ventricle catheter is positioned within the heart with the ventricle pacing electrodes in an apex location of a right ventricle chamber of the heart.
The atrial catheter has at least one atrial pacing electrode and at least one defibrillation electrode, both of which are electrically connected to the electronic control circuitry. In one embodiment, the atrial catheter has an atrial pacing electrode and a defibrillation electrode for sensing, pacing and defibrillating the atria of the heart. In an additional embodiment, the atrial catheter is positioned in the heart with the atrial pacing electrode in a supraventricular region of the heart and the defibrillation electrode in the right atrium chamber or a major vein leading to the right atrium of the heart.
According to one embodiment of the method of defibrillating the atria of the heart, when a supraventricular arrhythmia is detected, the electronic control circuitry delivers a synchronized pacing scheme of atrial and ventricular pacing pulses. The synchronized pacing scheme begins with an initial concurrent atrial and ventricular pacing pulse. The defibrillation system then proceeds to deliver a synchronized train of atrial pacing pulses through the atrial pacing electrode. In an alternative embodiment, the synchronized pacing scheme begins with a first atrial pacing pulse from the train of atrial pacing pulses being delivered to an atrial region of the heart upon detecting a ventricular R-wave through the ventricular catheter. Concurrent with delivering the train of atrial pacing pulses to the atrial region of the heart, the defibrillation system and method also deliver a series of ventricular pacing pulses to the ventricular region of the heart through the ventricular catheter.
The series of ventricular pacing pulses delivered to the ventricular region of the heart are synchronized with the delivery of the train of atrial pacing pulses to the atrial. The synchronization of the pacing pulses to the atrial and ventricular regions of the heart is based on a 1 to xe2x80x9cnxe2x80x9d ratio of ventricular pacing pulses to atrial pacing pulses, where xe2x80x9cnxe2x80x9d is an integer value greater than or equal to 3 and less than or equal to 50. The series of ventricular pacing pulses delivered to the ventricles help to stabilize the ventricular rhythm prior to the delivery of the atrial defibrillation electrical energy pulse.
At a predetermined coupling interval time after deliver in g a final atrial pacing pulse and a final ventricular pacing pulse, the atrial defibrillation electrical energy pulse is delivered across the atria of the heart. This atrial defibrillation pulse is timed so that the defibrillation electrical energy pulse falls outside the occurrence of a ventricular T-wave, thus reducing the chance of inducing ventricular fibrillation. As a result, the synchronized atrial defibrillation pulse of the present invention provides for a safer manner of treating atrial arrhythmias.